1. Field of the Invention
The present invention relates to a method for generating an alert, and more particularly relates to a method for automatically generating an alert when the level and frequency of signal vibration exceed a certain scale.
2. Description of the Related Art
To maintain a stable manufacturing process, signals generated in the manufacturing process are monitored. The signals may refer to the intensity of a light source used by a stepper required in the semiconductor manufacturing process, or the flow rate of etching solution used by a wet etching machine. Signal monitoring prevents products from being damaged by irregular operation.
Generally, signal monitoring is applied by predetermining upper and lower limits of so the signals. When the signals generated by process tools exceed the predetermined upper and lower limits, the monitor generates an alert to indicate the aberration in the apparatus such that the monitoring staff can take necessary action. FIG. 1 is a graph showing signals generated within a time interval by a process tool. In FIG. 1, all signals fall within a range between the upper and lower limits (i.e. 3.0 and 1.4 in FIG. 1). If the machine is using a general monitoring method, as a result, no alert is generated.
Although the signals fall within a range between the upper limit and lower limit, signal vibration may be an indicator of potential problems resulting in malfunction of process tools. When applying a general monitoring method that only employs upper and lower limits, not only signal vibration, but also potential problems are hidden.
The main object of the present invention is to provide a method for generating a signal vibration alert, wherein the vibration frequency is precisely calculated and a timely alert is provided to monitoring staff without interference from insignificant noise.
The method of the present invention collects a plurality of signals generated by a apparatus within a time interval. Based on the plurality of signals, a plurality of substantial swerves and of corresponding substantial edge-to-edge differences are recognized. Every three consecutive substantial swerves constitute a peak or a valley. Each substantial edge-to-edge difference is the edge-to-edge difference between every two consecutive swerves, and exceeds a predetermined noise range. Then, the frequency of the substantial edge-to-edge differences that exceed an acceptable range is calculated. If the frequency exceeds a predetermined frequency limit, an alert is automatically generated to indicate aberration in the apparatus.
In particular, the method of the present invention ignores signal variation resulting from noise, and focuses on recognizing the real vibration amplitude (i.e. substantial edge-to-edge difference) from signals generated. As soon as the substantial edge-to-edge differences exceed an acceptable range of the frequency limit, there may be potential problems concerning the operation of the apparatus.
The advantage of the present invention is that given signals do not exceed upper and lower limits; the method indicates the status of an apparatus by monitoring signal vibration and advances a timely alert to monitoring staff.